Chlorin and bacteriochlorin-based aminophenyl DTPA and N2S2 conjugates for MR contrast media and radiopharmaceuticals

ABSTRACT

Compositions that are chemical combination of porphyrins, chlorins, bacteriochlorins, and related tetra-pyrrolic compounds with radioactive elements such as Technetium 99 , Gadolinium, Indium 111  and radioactive iodine. When the element can form cations, the compound is usually a chelate with the porphyrin or chlorin structure. When the element forms anions, the compound is usually a direct chemical combination of the radioactive element into the porphyrin or chlorin structure. The invention further includes the method of using the compounds of the invention for diagnostic imaging of hyperproliferative tissue such as tumors and new blood vessel growth as is associated with the wet form of age related macular degeneration and methods of making the compounds. Compounds for MRI contrast imaging of the invention are usually Tc 99 , In 111  or Gd(III) complexes of compounds of the formula:

[0001] This application claims priority from Provisional PatentApplication No. 60/171,961 filed Dec. 23, 1999.

BACKGROUND OF THE INVENTION

[0002] Cancer is the second most common cause of death in the UnitedStates, accounting for 20% of all deaths. Until now, medicine has triedto overwhelm the cancer cell with brute force, slicing it out withsurgery, zapping it with radiation, or poisoning it with chemotherapy.All too often, however, a few cells survive the onslaught and germinate,sometimes years later, into tumors that are impervious to treatment. Iftumors can be diagnosed at early stages, it will certainly increase thesurvival rate of the cancer patients. Therefore, efforts are currentlyunderway in our and various other laboratories to develop efficienttumor diagnostic imaging agents.

[0003] For many years, in vivo imaging of human anatomy was dependentupon the intravenous administration of radioactive atoms (nuclearmedicine) or non-radioactive iodinated contrast media (various x-raytests and computed tomography). However, over the last decade magneticresonance imaging (MRI) has assumed a critical role in imaging, and,unlike x-rays or computed tomography, MR uses contrast media thatcontain paramagnetic ions, particularly Gadolinium [Gd(III)].Paramagnetic ions are not themselves “seen” by the MR scanner. Rather,they affect the water in body tissue so as to increase the “signal”emitted by tissue when it is placed in a magnetic field.

[0004] By and large, MR contrast media have been neitherdisease-specific nor organ-specific. Injected intravenously, most arerapidly excreted by the kidneys by glomercular filtration. Althoughseveral liver-specific contrast media have been created, other organshave not been successfully targeted, and no tumor-avid MR contrastagents are available to date.

[0005] Because of the importance of detection of unknown primary tumorand metastatic disease in diagnostic oncology imaging, a tumor-avid MRcontrast medium would have high implications for prognosis, therapyselection, and patient outcomes. The entire issue of cure versuspalliation would be impacted.

[0006] In recent years several reports focused on certain Gd-basedmacrocycles as potential magnetic resonance imaging (e.g. Z. D. Grossmanand S. F. Rosebrough, Clinical Radioimmunoimaging, Grune & StrattonInc., 1988, incorporated herein by reference as background art) and^(99m)Tc or ¹¹¹In chelated compounds as radiopharmaceuticals (e.g. H. D.Bums, R. F. Gibson, R. F. Dannals and P. K. S. Siegel (Eds.); Nuclearimaging in Drug Discovery, Development and Approval, Birkhauser, 1993,and G. B. Saha, Fundamentals of Nuclear Pharmacy, Springer-Verlag, 1992,incorporated herein by reference as background art).

[0007] Since the approval of [Gd(DTPA)(H₂O)]²⁻ in 1988, more than 30metric tons of Gadolinium have been administered to millions of patientsworldwide. Approximately 30% of MRI exams include contrast agents, andthis percentage is projected to increase as new agents and applicationsappear. Gadolinium is also finding a place in medical research. Over 600references to Gadolinium appear each year in the basic scienceliterature. While other types of MRI contrast agents, namely aniron-particle-based agent and a manganese (II) chelate have beenapproved, Gd(III) remains the dominant material. The reasons for thisinclude the direction of MRI development and the nature of Gd chelates.The signal intensity in MRI stems largely from the local value of thelongitudinal relaxation rate of water protons, 1/T₁, and the transverserate 1/T₂. Signal tends to increase with increasing 1/T₁ and decreasewith increasing 1/T₂. Pulse sequences that emphasize changes in 1/T₁ arereferred to as 1/T₁-weighed, and the opposite is true for T₂-weighedscans. Contrast agents increase both 1/T₁ and 1/T₂ to varying degrees,depending on their nature as well as the applied magnetic field. Agentssuch as Gadolinium (III) that increases 1/T₁ and 1/T₂ by roughly similaramounts are best visualized using T₁-weighted images, because thepercentage change in 1/T₁ in tissue is much greater than that in 1/T₂.The longitudinal and transverse relaxivity values r₁ and r₂ refer to theincrease in 1/T₁ and 1/T₂, respectively, per milliomole of agent. T₁agents usually have r₂/r₁ ratios of 1-2, whereas that value for T₂agents, such as iron oxide particles, is as high as 10 or more. Advancesin MRI have strongly favored T₁ agents and thus Gadolinium (III). Fasterscans with higher resolution require more rapid radio frequency pulsingand are thus generally T₁-weighed, since the MR signal in each voxelbecomes saturated. T₁ agents relieve this saturation by restoring a goodpart of the longitudinal magnetization between pulses. At the same timea good T₁ agent would not significantly affect the bulk magneticsusceptibility of the tissue compartment in which it is localized, thusminimizing any inhomogeneities which can lead to image artifacts and/ordecreased signal intensity.

[0008] The other important and interesting characteristic of Gadolinium(III) chelates is their stability. They remain chelated in the body andare excreted intact. For example, the off-the shelf ligands like DTPAform complexes so stable that while the agent is in vivo, there is nodetectable dissociation. Owing to their large size, lanthanides tend tofavor high coordination number in aqueous media. Currently, allGd(III)-based chelates approved for use in MRI are nine-coordinatecomplexes in which the ligand occupies eight binding sites at the metalcenter and the ninth coordinate site is occupies by a solvent watermolecule.

[0009] Radiopharmaceuticals are drugs containing a radionuclide and areused routinely in nuclear medicine department for the diagnosis ortherapy. Radiopharmaceuticals can be divided into two primary classes:Those whose biodistribution is determined exclusively by their chemicaland physical properties (like iodine-131) and those whose ultimatedistribution is determined by their biological interactions (like aradiolabeled antibody). The latter class includes more target-specificradiopharmaceuticals. A target-specific radiopharmaceutical consists offour parts: a targeting molecule, a linker, a chelating ligand and aradionuclide. The targeting molecule serves as the vehicle, whichcarries the radionucleide to the target site in diseased tissue. Theradionuclide is the radiation source.

[0010] Metallic radionuclides offer many opportunities for designing newradiopharmaceuticals by modifying the coordination environment aroundthe metal with a variety of chelators. Most of the radiopharmaceuticalsused in conventional nuclear medicine are ^(99m)Tc labeled, because ofits short half-life (6 hours) and ideal gamma emission (140 KeV).Millicurie quantities can be delivered without excessive radiation tothe patient. The monoenergetic 140-KeV photons are readily collimated,producing images of superior spatial resolution. Furthermore, ^(99m)TCis readily available in a sterile, pyogen-free, and carrier-free statefrom ⁹⁹MO-^(99m)TC generators. Its 6h half-life is sufficiently long tosynthesize the labeled radiopharmaceuticals, assay for purity, injectthe patient, and image yet short enough to minimize radiation dose.Another radionuclide successfully used is ¹¹¹In. The success of thepharmaceutical IN-DTPA-Octreotide (OCTREOSCAN), used for diagnosis ofsomatostatin receptor-positive tumors, has intensified the search fornew target-specific radiopharmaceuticals. Compared to ^(99m)Tc, thehalf-life of ¹¹¹In is much longer (72 hours).

[0011] Certain porphyrins and related tetrapyrrolic compounds tend tolocalize in malignant tumors and other hyperproliferative tissue, suchas hyperproliferative blood vessels, at much higher concentrations thanin normal tissues, so they are useful as a tool for the treatment ofvarious type of cancers and other hyperproliferative tissue byphotodynamic therapy (PDT) (T. J. Dougherty, C. J. Gomer, B. W.Henderson, G. Jori, D. Kessel, M. Kprbelik, J. Moan, Q. Peng, J. Natl.Cancer Inst., 1998, 90, 889 incorporated here by reference as backgroundart). However, most of the porphyrin-based photosensitizers includingPHOTOFRIN® (approved worldwide for the treatment of tumors) clear slowlyfrom normal tissue, so patients must avoid exposure to sunlight for asignificant time after treatment. In recent years, a number ofchlorophyll analogs have been synthesized and evaluated for their use asphotosensitizers for PDT (e.g. R. K. Pandey, D. Herman, Chemistry &Industry, 1998, 739 incorporated herein by reference as background art).Among these photosensitizers, the hexyl ether derivative ofpyropheophorbide-a 9 (HPPH) (e.g. R. K. Pandey, A. B. Sumlin, S.Constantine, M. Aoudia, W. R. Potter, D. A. Bellnier, B. W. Henderson,M. A. Rodgers, K. M. Smith and T. J. Dougherty, Photochem. Photobiol.,1996, 64, 194; B. W. Henderson, D. A. Bellnier, W. R. Graco, A. Sharma,R. K. Pandey, L. A. Vaughan, W. R. Weishaupt and T. J. Dougherty, CancerRes., 1997, 57, 4000; and R. K. Pandey, T. J. Dougherty, U.S. patent,1993, U.S. Pat. No. 5,198,460; U.S. patent, 1994, U.S. Pat. No.5,314,905 and U.S. patent, 1995, U.S. Pat. No. 5,459,159, incorporatedherein by reference as background art) and the hexyl-ether derivative ofpurpurin-18-N-hexylimide 10 (e.g. R. K. Pandey, W. R. Potter and T. J.Dougherty, U.S. patent, 1999, U.S. Pat. No. 5,952,366, incorporatedherein by reference as background art) have shown high tumor uptake andminimal skin phototoxicity compared with PHOTOFRIN®. HPPH is currentlyin phase I/II clinical trials for treatment of various types of cancerby photodynamic therapy at the Roswell Park Cancer Institute, Buffalo,N.Y. and the results are promising.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012]FIG. 1 shows an MR image control using a commercially availablecontrast agent vs. no use of contrast enhancement agent. The tumor areaof the images shows little or no enhancement using the commerciallyavailable contrast agent.

[0013]FIG. 2 shows the MR image using a Gd-HPPH contrast agent of theinvention vs. no contrast agent. The image formed using the contrastagent of the invention shows dramatic image enhancement of the tumorarea.

[0014]FIG. 3 is a graph of in vivo measurement of tumor vs. muscleuptake by reflection spectroscopy of the compound shown in FIG. 3.

[0015]FIG. 4 is a schematic diagram showing chemical synthesis of4-aminophenyl DTPA penta-tert-butyl esters.

[0016]FIG. 5 is a schematic diagram showing chemical synthesis ofcarboxy 3-(hexyloxy)ethyl pyropheophorbide-a from methylpheophorbide-a.

[0017]FIG. 6 is a schematic diagram showing chemical synthesis ofHPPH-aminophenyl DTPA from carboxy 3-(hexyloxy)ethyl pyropheophorbide-aand 4-aminophenyl DTPA penta-tert-butyl ester followed by reaction withGadolinium (III) trichloride to form HPPH-aminophenyl DTPA.

[0018]FIG. 7 is a schematic diagram showing chemical synthesis ofpurpurin-18-imide-Gd(III) aminophenyl DTPA (16).

[0019]FIG. 8 is a schematic diagram showing preparation of Gd(III)aminophenyl DTPA complex from purpurin 7.

[0020]FIG. 9 is schematic diagram showing preparation of bacteriochlorinbased Gd(III) aminophenyl DTPA.

[0021]FIG. 10 is a schematic formula for bisaminoethanethiol compound23.

[0022]FIG. 11 is a schematic formula for bisaminoethanethiol compound24.

[0023]FIG. 12 is a schematic diagram showing preparation of HPPH basedbisaminoethanethiol conjugate 27.

[0024]FIG. 13 is a schematic diagram showing preparation of HPPH basedIn Aminophenyl DTPA conjugate 28.

[0025]FIG. 14 is a schematic diagram showing preparation of N₂S₂ ligand^(99m)Tc complex, Aminophenyl DTPA ¹¹¹In complex and Aminophenyl DTPAGd(III) complex, e.g. 3-devinyl-3-(1′-alkoxyethyl)-17-[3′-(4″-amidobenzyl gadolinium(III)DTPA)]ethylpyropheophorbide-a, from a DTPA or N₂S₂ dihydro tetrapyrrole compound ofthe invention.

[0026]FIG. 15 is a schematic diagram showing N₂S₂ ligand ^(99m)Tccomplex, Aminophenyl DTPA “In complex, and Aminophenyl DTPA ¹¹¹InComplex, and Aminophenyl DTPA Gd(III) complex, e.g.purpurin-18-(30devinyl-3-(4″-amidobenzyl gadoliniumDTPA)]-N-substitutedimide, from a DTPA or N₂S₂ dihydro tetrapyrrole compound of theinvention.

[0027]FIG. 16 is a schematic diagram showing N₂S₂ ligand ^(99m)Tccomplex, Aminophenyl DTPA “In complex, and Aminophenyl DTPA ¹¹¹InComplex, and Aminophenyl DTPA Gd(III) complex, e.g.purpurin-18-(3-devinyl-3-(1′alkoxy ethyl)-17-[3′-(4″-amidobenzylgadolinium(III)DTPA)]ethyl pyropheophorbide-a, from a DTPA or N₂S₂dihydro tetrapyrrole compound of the invention.

[0028]FIG. 17 is a schematic diagram showing N₂S₂ ligand ^(99m)Tccomplex, Aminophenyl DTPA “In complex, and Aminophenyl DTPA ¹¹¹InComplex, and Aminophenyl DTPA Gd(III) complex, e.g. bacteriopurpurin18-3-(alkyl or alkoxyalkyl)-7-keto-17-[3′-(4″-amidobenzylgadolinium(III)DTPA)]-N-substituted imide, from a DTPA or N₂S₂tetrahydro tetrapyrrole compound of the invention.

BRIEF DESCRIPTION OF THE INVENTION

[0029] The invention includes compositions that are chemical combinationof porphyrins and chlorins and related tetra-pyrrolic compounds withradioactive elements such as Technetium⁹⁹, Gadolinium, Indium¹¹¹ andradioactive iodine. When the element can form cations, the compound isusually a chelate with the porphyrin or chlorin structure. When theelement forms anions, the compound is usually a direct chemicalcombination of the radioactive element into the porphyrin or chlorinstructure.

[0030] Examples of porphyrin and chlorin structures that can formcompounds with radioactive elements, when modified in accordance withthe present invention, are for example described in U.S. Pat. Nos.5,756,541; 5,028,621; 4,866,168; 4,649,151; 5,438,071; 5,198,460;5,002,962; 5,093,349; 5,171,741; 5,173,504; 4,968,715; 5,314,905;5,459,159; 5,770,730; 5,864,035; 5,190,966; and 5,952,366 all of whichare incorporated by reference as background art.

[0031] The invention further includes the method of using the compoundsof the invention for diagnostic imaging of hyperproliferative tissuesuch as tumors and new blood vessel growth as is associated with the wetform of age related macular degeneration.

[0032] Unexpectedly, porphyrins and chlorins, as above described, uponinjection, carry the radioactive element into cells ofhyperproliferative tissue and dramatically enhance the signal producedby tumor tissue in MR imaging.

[0033] It is to be understood that porphyrin and chlorin compounds(including bacteriochlorins) may be chemically altered to other forms bysubstitutions and modifications; provided that, the base tetrapyrrolicstructure that allows selective entry and retention inhyperproliferative tissue cells (e.g. tumors) is retained.

[0034] Compounds of the invention usually have the formula

[0035] In the above formula,

[0036] (CH₂)₂CONHphenylene CH₂DTPA,

[0037] or

[0038] where R₉=—OR₁₀ where R₁₀ is lower alkyl of 1 though 6 carbonatoms; R₂ is —CH₃, R₅ is —CH₂CH₃, and R₃ and R₄ together form a covalentbend or R₂ and R₃ together are =0, R₄ is —CH₂CH₃ and R₅ is —CH₃; R₆ is

[0039] or a covalent bond; R₇ is ═O when R₆ is

[0040] and R₇ is a covalent bond; and R₈ is —(CH₂)CO₂CH₃,—(CH₂)₂CONHphenyleneCH₂DTPA,

[0041] R₁₁ is lower alkyl of 1 through 6 carbon atoms,—(CH₂)₂CONHphenyleneCH₂DTPA,

[0042] provided that only one of R₁, R₈ or R₁₁ is—(CH₂)₂CONHphenyleneCH₂DTPA,

DETAILED DESCRIPTION OF THE INVENTION

[0043] An objective of the invention was to use these photosensitizersas a vehicle for delivering the desired conjugate (chelated with Gd orradionuclides) to tumor. The chelate is “bifunctional” because, it bindsthe Gd at one end and binds the target specific vehicle at the other.The chelate is a multidentate ligand, which has appropriate ligatinggroups for coordination to the metal. In a preferred embodiment, ourinvention includes:

[0044] Development of chlorin and bacteriochlorin-basedGd(III)aminophenyl DTPA conjugates with variable lipophilicity as tumordiagnostic agent by MRI.

[0045] Development of chlorin and bacteriochlorin-based ¹¹¹Inaminophenyl DTPA and ^(99m)Tc N₂S₂ conjugates with variablelipophilicity as tumor diagnostic radiopharmaceuticals.

[0046] A goal has been: (i) to successfully bind Gadolinium to atumor-avid porphyrin, originally designed for photodynamic therapy(PDT), and to prove that striking tumor uptake at 24 hours enhances the“signal” produced by tumor, thus dramatically increasing its conspicuityon MR imaging and (ii) to prepare related ^(99m)Tc and ¹¹¹In labeledradiopharmaceuticals as diagnostic agents for nuclear medicine.

[0047] This invention includes the synthesis and application of certainchlorin and bacteriochlorin-based bisaminoethanethiol (N₂S₂) andmodified ditetratriethylamine penta carboxylic acid (DTPA) conjugates asMR contrast media and radiopharmaceuticals for diagnosis of primarymalignancy and metastatic disease.

[0048] The following examples describe examples for synthesis and use ofmagnetic resonance imaging agents. Synthesis ofHPPH-Gd(III)aminophenylDTPA 14: For the preparation of the titlecompound, pyropheophorbide-a 6b was obtained from methylpheophorbide-a6a (which in turn was extracted from Spirulina Algae) by following theliterature procedure. It was then converted into methyl3-(hexyloxy)ethyl analog 9a by following a methodology developed in ourlaboratory. Hydrolysis of the methyl ester functionality with aqueousLiOH/methanol/THF produced the corresponding carboxylic acid 9b inquantitative yield. The reaction of 9b with 4-aminophenyl DTPApenta-tert-butyl esters prepared by following the methodology in FIG. 4via the carbodiimide approach (R. K. Pandey, F. -Y. Shiau, A. B. Sumlin,T. J. Dougherty and K. M. Smith, Bioorg. Med. Chem. Lett., 1994, 4,1263, incorporated herein by reference as background art) produced thecorresponding analog 12 in 57% yield (FIGS. 5 and 6). The structure wasconfirmed by NMR and mass spectrometry analyses.

[0049] Before preparing the Gd(III) complex, the tert-butyl groups inconjugate were converted into corresponding carboxylic acid by reactingwith trifluoroacetic acid (yield 100%). For the preparation of Gd(III)complex 14, the conjugate was dissolved in pyridine and Gadoliniumchloride hexahydrate dissolved in deionized water. The mixture wasstirred at room temperature for 2h. After the completion of the reaction(monitored by TLC), pyridine was removed under high vacuum. The residuewas washed with water to remove the excess of Gadolinium chloride, driedunder vacuum and the title compound was isolated in 92% yield. Thestructure of the final product was confirmed by mass spectrometry.

[0050] Synthesis of Purpurin-18-imide-Gd(III)aminophenylDTPA 16:Methylpheophorbide-a 7a was converted into the hexylether derivative ofN-hexyl purpurinimide in 70% yield. The methyl ester group was thenhydrolyzed to the corresponding carboxylic acid 10 by following themethodology as discussed for the preparation of 9b. Purpurin-imide 10was then reacted with aminophenylDTPA penta tert-butyl ester 5 byfollowing a reaction sequence depicted in FIG. 7 and the intermediateconjugate was isolated in 45% yield. Further reaction withtrifluoroaceticacid and then with GdCl₃.6H₂0 produced the Gd(III)complex 16 in >90% yield. The structures of the conjugates wereconfirmed by NMR and mass spectrometry.

[0051] In our attempt to investigate the effect of the position of theGd(III) conjugate in the macrocycle, purpurin-imide 7 was converted intothe related carboxylic acid analog 11 by conventional procedures.Reaction of 10 with aminophenyl DTPA 5 will produce Gd(III) aminophenylDTPA conjugate 15, purpurin 18-3-devinyl-3[4′-amidophenyl Gadolinium(III) DTPA]-N-hexylimide.

[0052] In this series of compounds, the overall lipophilicity of themolecule can be altered by varying the length of the carbon chain ofeither the alkyl ether substituents and/or N-substituted alkyl chain.Thus, these compounds provide a unique opportunity to investigate thecorrelation of tumor uptake and lipophilicity.

[0053] Synthesis of Bacteriochlorin BasedGD(III)aminophenylDTPA 22:

[0054] Bacteriochlorins are a class of tetrapyrroles in which the twopyrrole units diagonal to each other are reduced. Starting fromN-hexyl-purpurin imide 7 we have prepared ketobacteriochlorin 20 byfollowing a reaction sequence illustrated in FIG. 9. In our approachpurpurinimide 7 containing a vinyl group at position 3 was convertedinto the 3-devinyl-3-ethyl analog 17 (also be named asmeso-N-hexyl-purpurin-18-imide) by reacting with hydrogen using Pd/C asa catalyst. It was then reacted with osmiumtetroxide/pyridine/H₂S (A. N.Kozyrev. T. J. Dougherty and R. K. Pandey, Tetrahedron Lett., 1996, 37,3781, incorporated herein by reference as background art) and thecorresponding vic-dihydroxybacteriochlorin 18 was isolated in 75% yieldas a mixture of diasteriomers (cis-hydroxy groups up or down relative totrans-reduced ring D). The dihydroxy analog as a diasteriomeric mixturewas treated with sulfuric acid under pinacol-pinacolone reactionconditions, (R. K. Pandey, T. Tsuchida, S. Constantine, G. Zheng, C.Medforth, A Kozyrev, A. Mohammad, M. A. J. Rodgers, K. M. Smith and T.J. Dougherty, J. Med. Chem., 1997, 40, 2770, incorporated herein byreference as background art) and the ketobacteriochlorin, containingketo- group either at 7- (compound 20) or 8-position (compound 19)respectively were isolated in 70% yield. Among these bacteriochlorins,the 7-keto analog 20 showed high tumor uptake as determined by in vivoreflectance spectroscopy in mice model transplanted with RIF tumor (seeFIG. 3). The structures of bacteriochlorins 19 and 20 were confirmed byNMR and mass spectrometry analyses.

[0055] Our next step was to hydrolyze the methyl ester group inpurpurinimide 20 into carboxylic acid 21 before converting it into thecorresponding 4-aminophenylDTPA conjugate 22 by following themethodology discussed previously for the preparation of related HPPH andpurpurin-imide analogs.

[0056] Synthesis of HPPH-based Bisaminoethanethiol Conjugates 27:

[0057] For preparing the ^(99m)Tc labeled radiopharmaceuticals, twoaminobisethanethiols 23 and 24 were prepared by following themethodology developed in our laboratory (G. Li, Q. Ma, B. Ma, Z. D.Grossman and R. K. Pandey, Heterocyclics, 1999, in press; and G. Li, B.Ma, J. R. Missert, Z. D. Grossman and R. K. Pandey, Heterocyclics, inpress, incorporated herein by reference as background art). For thesynthesis of N ₂S₂ conjugate 26, HPPH was reacted with N₂S₂ chelate 23and the thioprotected HPPH conjugate 25 was isolated in 40% yield.Subsequent deprotection of the thiols with triethysilane/TFA affordedthe corresponding bis-aminoethanethiol 26 in quantitative yield. Thestructure of the newly synthesized compound was confirmed by NMR andmass spectrometry analyses.

[0058] The Tc-99m complex 27 was prepared by ligand-exchange reactionwith ^(99m)Tc pertechnatate reduced by Sn(II)glucoheptonate by followingthe methodology of Kung and coworkers (S. K. Meegalla, K. Plossl, M-P.Kung, S. Chumpradit, D. A. Stevenson, S. A. Kushner, W. T. McElgin, P.D. Mozley and H. F. Kung. J. Med. Chem., 1997, 40, 9, incorporatedherein by reference as background art). The radiolabeling yieldwas >80%. The purity of the Tc-99m complex was >95%, by chromatography.

[0059] Syntheses of HPPH based ¹¹¹In AminophenylDTPA Conjugate 28:

[0060] For the preparation of the title compound, theHPPH-aminophenylDTPA 13 was reacted with ¹¹¹In(III) chloride, followingthe methodology reported by Low and coworkers (S. Wang J. Juo, D. A.Lantrip, D. A. Waters, C. J. Mathias, W. A. Green, P. L. Fuchs and P. S.Low, Bioconjugate Chem., 1997, 8, 673, incorporated herein by referenceas background art) for the preparation of ¹¹¹In DTPA-Folate and the¹¹¹In labeled compound was obtained in 82% yield.

[0061] Body Tumor MR Imaging:

[0062] HPPH-Gd(III)AminophenylDTPA Conjugate 14:

[0063] Following the synthesis of GD-labeled HPPH, a series of threerats were injected intravenously and studied immediately afterinjection, at 1 hour, and at 24 hours, to establish whether the Gd-HPPHremained in the circulation longer than the current standard contrastmedium (Magnavist or Gd-DTPA).

[0064] Whereas Magnavist clears rapidly from the mammalian circulationby glomerular filtration, with a circulatory half-time of 16-20 minutes,the newly-synthesized contrast medium Gd-HPPH, was evident in thecerebral circulation at 1 hour. Subsequently, to establish whether theGD-HPPH is tumor-avid, a single rat with a subcutaneously-implanted Wardcolon carcinoma was imaged, 24 hours after intravenous GD-HPPH, A secondtumor-bearing rat was imaged 24 hours after injection of Magnavist (SeeFIGS. 1 and 2). Clearly, the enhanced tumor signal after Gd-HPPHinjection indicated that GD-HPPH 14 has potential as a contrast mediumfor MR. HPPH (a chlorophyll- a derivative) represents the vehicle bywhich the Gd complex is carried into the tumor. Addition of the Gdchelate to HPPH does not hinder its ability to form singlet oxygenproducing efficacy, so this contrast medium also has the potential fordual action: enhanced localization on MR imaging (diagnosis), followedby directed light exposure with tumor injury (treatment). Also, becauseof its excellent tumor selectivity and high fluorescence, the newlysynthesized conjugate can be used for IR imaging. Also, Indium or otherradionuclides like Tc-99m (the latter conjugated by an N₂S₂ ligand)bound to chlorins and bacteriochlorins synthesized and proposed in thisinvention have potential as imaging agents for nuclear medicine.

What is claimed is:
 1. A compound of the formula

—(CH₂)₂CONHphenyleneCH₂DTPA,

where R₉=—OR₁₀ where R₁₀ is lower alkyl of 1 though 6 carbon atoms; R₂is —CH₃, R₅ is —CH₂CH₃, and R₃ and R₄ together form a covalent bend orR₂ and R₃ together are =0, R₄ is —CH₂CH₃ and R₅ is —CH₃; R₆ is

or a covalent bond; R₇ is ═O when R₆ is

and R₇ is a covalent bond; and R₈ is —(CH₂)CO₂CH₃,—(CH₂)₂CONHphenyleneCH₂DTPA,

R₁₁ is lower alkyl of 1 through 6 carbon atoms,—(CH₂)₂CONHphenyleneCH₂DTPA,

provided that only one of R₁, R₈ or R₁₁ is —(CH₂)₂CONHphenyleneCH₂DTPA,


2. The compound of claim 1 where R₁, R₈ or R₁₁ is


3. The compound of claim 1 where R₁, R₈ or R₁₁ is—(CH₂)₂CONHphenyleneCH₂DTPA.
 4. The compound of claim 2 where R₈ is


5. The compound of claim 3 where R₈ is —(CH₂)₂CONHphenyleneCH₂DTPA. 6.The compound of claim 5 where R₂ is —CH₃ and R₅ is —CH₂CH₃.
 7. Thecompound of claim 1 where R₆ is


8. The compound of claim 7 where R₆ is

where R₁₀ is hexyl.
 9. A Technetium^(99m) complex of the compound ofclaim 2 .
 10. An Indium¹¹¹ complex of the compound of claim 3 .
 11. AGadolinium(III) complex of the compound of claim 3 .
 12. The compound ofclaim 9 wherein the compound is a ^(99m)Tc bisaminoethanethiol analog ofHPPH.
 13. The compound of claim 10 wherein the compound is a ¹¹¹Inaminophenyl DTPA analog of HPPH.
 14. The compound of claim 11 whereinthe compound is HPPH-Gd(III)aminophenylDTPA
 15. The compound of claim 11wherein the compound is purpurin 18 imide-Gd(III)aminophenylDTPA. 16.The compound of claim 11 wherein the compound is aGd(III)aminophenylDTPA analog of bacteriochlorin.
 17. A method for thepreparation of the compound of claim 14 which comprises: hydrolizingmethyl 3-(hexyloxy)ethyl pheophorbide a with an aqueous solution ofLiOH, methanol and tetrahydrofuran to obtain the correspondingcarboxylic acid; reacting the carboxylic acid with 4-aminophenyl DTPApenta-tert-butyl ester to produce the tert-butyl aminophenyl DTPAanalog; reacting the DTPA analog with trifluoroacetic acid to convertthe tertiary butyl groups to carboxylic acid groups; reacting with asolution of Gadolinium hexahydrate.
 18. A method for the preparation ofthe compound of claim 15 which comprises: hydrolizing a methyl estergroup of the hexylether derivative of N-hexyl purpurinimide to thecorresponding carboxylic acid; reacting the resulting carboxy purpurinimide with a solution of aminophenylDTPA penta-tert-butyl ester;reacting the resulting conjugate with trifluoroacetic acid to obtain acarboxylic acid; and reacting the resulting carboxylic acid withGadolinium chloride to obtain the desired compound.
 19. A method for thepreparation of the compound of claim 16 which comprises: hydrogenating 3vinyl purpurinimide 7 to obtain meso-N-hexyl-purpurin-18-imide; reactingthe meso-N-hexyl-purpurin-18-imide with osmiumtetroxide, pyridine andH₂S to obtain vic-dihydroxybacteriochlorin; reacting thevic-dihydroxybacteriochlorin with sulfuric acid to obtain a7-ketobacteriochlorin; hydrolizing a methyl ester group in the7-ketobacteriochlorin to a carboxy group; reacting the carboxy7-ketobacteriochlorin with aminophenylDTPA penta-tertiary butyl ester;reacting the resulting product with trifluoroacetic acid to obtain thecorresponding carboxylic acid DTPA analog; and reacting the carboxy DTPAanalog with Gadolinium chloride to obtain the desired compound.
 20. Amethod for the preparation of the compound of claim 12 which comprises:reacting HPPH with aminobisethanethiol to obtain a thioprotected HPPHconjugate; reacting the conjugate with triethylsilane and TFA todeprotect the thiols; and reacting the conjugate with deprotected thiolswith ^(99m)Tc pertechnatate reduced by Sn(II) glucoheptonate to obtainthe desired compound.
 21. A method for the preparation of the compoundof claim 12 which comprises: reacting HPPH-aminophenylDTPA with¹¹¹In(III)chloride to obtain the desired compound.